1. Field of the Invention
This invention relates to curable epoxy resins and more particularly to epoxy resins containing certain polyether thioureas having terminal primary amino groups.
2. Prior Art
Epoxy resins constitute a broad class of polymeric materials having a wide range of physical characteristics. The resins are characterized by epoxide groups which are cured by reaction with certain catalysts or curing agents to provide cured epoxy resin compositions with certain desirable properties. The most commonly used curing agents are aliphatic amines such as diethylenetriamine, triethylenetetramine and the like.
Epoxy resin compositions having improved physical properties are obtained by employing polyoxyalkyleneamines, and polyoxyalkylenediamines in particular, as curing agents. However, such epoxy resin compositions require long curing times. It is therefore common to employ with such epoxy resin compositions a co-curing agent such as those described in U.S. Pat. No. 3,549,592.
Also known to be effective as epoxy resin curing agents or co-curing agents are various ureas and substituted ureas, such as those disclosed in U.S. Pat. Nos. 3,294,749; 2,713,569; 3,386,956; 3,386,955; 2,855,372 and 3,639,338. However, for certain resin applications where high tensile shear strength, high flexural strength and a high ultimate elongation is required, none of the above curing agent compositions have been entirely adequate.
It has now been found that certain polyether thioureas having terminal primary amino groups, when employed as epoxy curing agents provide cured epoxy resin compositions exhibiting outstanding physical properties. Specifically, epoxy resin formulated with these curing agents and cured, will provide an epoxy resin with high tensile shear strength, high flexural stength and high ultimate elongation thus alleviating the previously mentioned disadvantages. Such cured epoxy resin compositions are useful as coatings, castings, sealants and adhesives.